Creating a Subnet Group

When you create a new subnet group, note the number of available
IP addresses. If the subnet has very few free IP addresses, you might be
constrained as to how many more nodes you can add to the cluster. To
resolve this issue, you can assign one or more subnets to a subnet group
so that you have a sufficient number of IP addresses in your cluster's
Availability Zone. After that, you can add more nodes to your
cluster.

The following procedures show you how to create a subnet group called
mysubnetgroup (console), the AWS CLI, and the
ElastiCache API.

In the Create Subnet Group wizard,
do the following.
When all the settings are as you want them, choose Yes, Create.

In the Name box,
type a name for your subnet group.

In the Description box,
type a description for your subnet group.

In the VPC ID box,
choose the Amazon VPC that you created.

In the Availability Zone and Subnet ID lists,
choose the Availability Zone and ID of your private subnet,
and then choose Add.

In the confirmation message that appears, choose Close.

Your new subnet group appears in the Subnet Groups list of
the ElastiCache console. At the bottom of the window you can choose the subnet
group to see details,
such as all of the subnets associated with this group.

Creating a Subnet Group (AWS CLI)

At a command prompt, use the command create-cache-subnet-group to create a subnet group.